SU964917A2 - Dc vl-to-three phase ac voltage converter - Google Patents

Description

(54) CONVERTER CONVERTER CONDITION TO THREE-PHASE VARIABLE

one

The invention relates to electrical engineering and can be used in power supply and electric power systems for converting a constant voltage to a three-phase alternating voltage of a stepwise quasi-sinusoidal form.

According to the main author. St. No. 868953 is known for a three-phase variable direct current voltage converter, containing a single-phase inverter, a transformer, the primary winding of which is connected to the output of the inverter, and the secondary through alternating current switches with the output terminals of the converter, each phase includes two parallel-connected secondary windings one of these windings is made with an intermediate tap, one end of a pair of windings of each phase together with an intermediate tap of one of its windings is connected to the corresponding one one phase connection of the transducer through the License keys

alternating current, and the other ends of the winding pairs of each of the phases are connected to the corresponding neighboring high-. to the input phase output of the transformers directly. Output linear voltage has a five-step form. The first three stages are formed by connecting to the output terminals of the converter of the sections of secondary ob-, coil, voltage, on which

10, respectively, to the amplitudes of these steps, and the fourth and fifth steps are formed by summing up the voltage of the two sections of the HE phase; The disadvantage of this transform body is the non-sinusoidal shape of the output voltage curve, which contains higher harmonics with consecutive numbers 17,19,35,37. And the harmonic ratio of this voltage of 20 is 10.1%. This leads to increased power losses in the consumer and the need to install output filters, which increase the mass of the 396 and the dimensions of the converter, worsen the efficiency, the speed of the converter-load system, the symmetry of the output voltages, the stiffness of the external characteristic. The purpose of the invention is to improve the cnKt of the N-step output voltage waveform, where N is the number of steps in the half-cycle of the output voltage, with all additional taps from the alternating current connected to the output of this phase of the converter. The goal is achieved by the fact that in a DC to three-phase AC converter one of the secondary windings of each phase contains additional N / 6-2, and another N / 6-1 taps with even N and M-9 taps with odd N, where N is the number of steps in the half-cycle of the output voltage, with all additional taps connected to the output switches of this phase of the converter via AC switches. FIG. 1 shows a converter circuit; in fig. 2 - voltage waveforms on the transformer windings, j time diagram of the key controlled pulses and voltage form on the load for N 15. The three-phase converter contains a single-phase inverter 1, the output of the second is connected to the primary winding of the transformer 2, section 3-7 of the secondary windings through which keys 8-22 of alternating current are connected to the output terminals of the converter A, B, C. As alternating current keys can be used triacs, alternating-connected thyrisors or transistors with diodes, transistors, included in the diagonal DC diode bridges. Operation of the converter for active-inductive nag (euzku when forming the output linear voltage with the number of steps in the half-period N 15 (figure 2) is considered. The device works as follows. The single-phase inverter 1 operates at a frequency 15 times the output frequency. This converter generates an alternating voltage on the transformer windings, the shape of which is shown in Fig. 2 (o). The keys are controlled by voltage pulses, the diagram of which is preceded by 7,4, is shown in Fig. 2 ((D). Moreover, the pulses appropriate Graphics 8 are supplied to key 8, graphics 9 to key 9, etc. To obtain an output voltage converter, close in shape to a sinusoidal one, the amplitudes of its steps are chosen from the condition for excluding harmonics close to the main one. secondary windings of the transformer of each phase, for example, containing sections 3 5 7, participate in the formation of odd linear stages;} at intervals O - 7G / 3, each half-period, and the other phase windings containing sections and 6 - in the formation of odd linear stages voltage on the floor their same intervals. For N 15 - FIG. 2 (5). The voltages of the 3- (Ucj, Uc7) sections are related to the amplitudes of the output linear voltage steps (U -U ..) as follows (A) (11;) 0, C5 QcB - U r, SiH (S: / ) Uj with isb-and vistp / zo} -,. C9Tr / 30) - U5 where Tsu is the amplitude of the approximating sinusoid passing through the midpoints of the horizontal portions of the steps (Fig. 2). in general, for any odd to obtain a sinusoidal law of amplitude change. The steps of the number of turns of the sections of the first and second windings of each phase (W-,), counted relative to one of their extreme conclusions, should be associated respectively with the total numbers of turns of each of the windings ( W, W / j) ratios:,.,., Mf ± ..-) -ErifiiS, SiMf Jgj.) Where 1 1,2,3 ... for the first winding; , 2,3 ...-: - for the second winding, ja for even N, these relations have the form,. .Mflil 41 -) sXf-isMf-) N 1 194 I i, t., J ...-. l- 2. At intervals of each cycle, the linear voltages are formed by summing the voltages of sections 3-7 of two phases, for example, for N 15, the sixth, seventh and eighth steps of voltage 0 are formed in the following way (MG). ) sgCs)),, 7 (Av) cl (b) c6tc) with the CCES. ) -UcbC6 Jc5e8; cb (.c) 4u5 -:. Dei (dv) .i -, (ДЗ ,, and amplitudes of the seventh and eighth steps of the linear voltage; voltage at C31c) C7 (B) sections from the third to the seventh phase B; cttc) c5 (c1 voltage across sections 3, phase C. The half-period of the output voltage of the converter can be divided into 15 equal intervals. In the first interval, the keys 8 and 22 are closed (Fig. 2.6). Section 3 phases with voltage U through key 8 and section 3. JS of phase C with a flashing voltage Ug- through key 22 is connected to the output pins of converter A and B, C and A, respectively. As a result, the first positive, pole negative and voltage goes ,, Ugt, UCA. 7, 6 On the second interval, the polarity of the voltage on the windings changes t transformer 2, switches 9 and 21 are closed, and section 4 of phase A with voltage and through key 9 and section 2 and phase C with common voltage Ujj are connected to the same output terminals of the converter. positive, seventh negative and fourth positive voltage step Od, (CA In the third interval, the polarity of the voltage on the transformer windings changes again, closing switches 10 and 20. Sections 3 and 5 of phase A with common, voltage 1) 3 through a switch 10 are connected to the output pins A and B, and sections 3 and -5 phases C through switch 20 also with a common voltage U - to conclusions C and A. As a result, a third is formed positive, the eighth is negative, and a third is positive, C, and. voltage levels U., Ц,, гд “At the next intervals, the operation of the converter occurs similarly in accordance with the diagram of key control pulses. 8, as a result of the operation of the converter, a three-phase eight-step voltage is generated at its output (Fig. 2, -i). When the load is connected by a star, the phase voltages have a seven-step form with zero pause and double the average duration of the stage. Connecting any branch of the circuit using alternating current switches provides the possibility of its passage in two directions and the constant potential difference of the phases during each interval. This determines the efficiency of the converter at any load power factor with a constant output voltage curve. The proposed converter, in comparison with the prototype, has the best spectral composition of the shape of the output voltage curve. In the considered case, when N 15, the output voltage contains higher harmonics with the serial numbers n 29, 31, 59.61 ..., and the harmonic coefficient of this voltage is K 6.05%. The advantage of the proposed circuit is 4 times. It is also that it allows a significant improvement in the shape of the output voltage curve without significantly complicating the circuit. . .

When a converter in one phase is added to one phase from one of the secondary windings of the transformer and one AC key, the number of steps in the half period increases by three, and the numbers of each pair of harmonics present in this voltage increase by 6i, where 1 1,2,3 ... the number of a pair of harmonics. By increasing the number of winding leads, it is possible to form a three-phase voltage with a large number of stages and to obtain an almost sinusoidal shape without output filters.

This reduces the mass and dimensions by increasing the operating frequency of the transformer and eliminating output filters, increases efficiency and speed, improves the symmetry of the output voltages and their independence from the magnitude and nature of the load by eliminating the output filters. The absence of the latter; also eliminates possible auto-oscillations in the converter-load system. In addition, reactive load power is more fully compensated. Critical load power factor; up to which full reactive compensation takes place

power, the source of constant input voltage, decreases to 0.105 with N 15 instead of

Cos if.

0,175 in the prototype. With

As the N increases further, the coefficient CCrc tends to zero.

Claims (1)

1. USSR author's certificate No. 868953, cl. H 02 M, 1979. lpn. N n